The Pathology Laboratory Core of the Children's Hospital of Philadelphia is a core facility that provides a full range of services for morphologically based studies, ranging from routine histology to complex image analysis, aser capture microdissection, and tissue microarray preparation and analysis. Services include preparation of animal and human tissues for microscopic analysis including paraffin embedding and sectioning, and cryosectioning. The Core also provides services for detection of transgenes and transgene products including in situ hybridization and immunohistochemistry. This Core is directed by a board-certified anatomic pathologist, Dr. Alex Judkins, with additional pathologists on staff, providing optimal expertise for interpretation of results, troubleshooting of procedures, and development of new assays. (This facility is also staffed by clinically trained histotechnologists, with expertise in tissue processing, including frozen sections, histochemistry, and immunohistochemistry). This Core has a track record of productive interaction with the investigators of Projects 1, 2, and 4, and for the proposed PEGT will also provide services for Projects 3 and 5. The Cores najor assets include state-of-the-art equipment (laser capture microdissection), innovative techniques (tissue microarray), and an interactive and knowledgeable staff with considerable experience and expertise in characterizing new antibodies for immunohistochemistry. The Core is structured so that core personnel can provide services on a fee-for-service basis, or if they prefer, investigators can use the core's facilities to perform the studies themselves with training, advice and assistance provided as needed by the core staff. Because of the organizational structure already in place, this core is well qualified to serve as a shared resource for all the PEGT's and for other NHLBI-funded investigators.